Method for applying a reinforcement of  metal material to a component of metal  material, particularly in the construction of a motor-vehicle body or a sub-assembly thereof

ABSTRACT

A structural joint between two components of metal material is obtained by carrying out an electrical resistance welding spot between said components and subsequently performing a step of applying a cladding of metal material by an additive manufacturing technology. In one example, after a first step of applying a coarse base cladding, a second step of applying a fine cladding is carried out, again by additive manufacturing technology. The fine cladding can include a distribution of stiffening micro-ribs above the base cladding. The same method can also be applied to a single sheet metal component, rather than to a welded joint.

FIELD OF THE INVENTION

The present invention relates to methods for applying a reinforcement ofmetal material to one or more components of metal material, particularlyin the construction of a motor-vehicle body or a sub-assembly thereof.

PRIOR ART

Applying a reinforcement of metal material above one or more componentsof metal material by means of “additive manufacturing” technology hasalready been proposed. This technology has been known and used for sometime. It makes use of an energy source, such as a laser beam, to meltlayers of metal powders in such a way as to form a metal part with adesired configuration, layer by layer. A machine for producing metalcomponents by means of “additive manufacturing” technology is, forexample, described and illustrated in the document WO 2015 181772A1.

Object of the Invention

The main object of the present invention is to identify new methods forapplying metal reinforcements to one or more metal components, throughthe use of “additive manufacturing” technology, particularly in themanufacture of motor-vehicle bodies or sub-assemblies thereof.

In particular, one object of the invention is to identify new methods ofproducing metal structures, in particular motor-vehicle structures andsub-assemblies thereof, which allow significant improvements both interms of lightness and in terms of strength of the obtained structure.

Another object of the invention is to achieve the aforesaid objectiveswith a method that is easily adaptable in current production lines ofmotor-vehicles and that, consequently, does not entail high costs forthe implementation thereof.

Another object of the invention is that of optimizing, in particular,the manufacture of a motor-vehicle “body-in-white” (BIW), allowing thebody to be framed by applying a limited number of electrical resistancewelding spots.

Yet another object of the invention is to provide alternativemanufacturing techniques for producing molded metal sheet components, inparticular motor-vehicle components.

SUMMARY OF THE INVENTION

In the present description and in the claims that follow, the term“additive manufacturing” is used to mean a method in which an energysource is used, such as a laser or plasma beam, to selectively meltlayers of metal powders, or metal wires, of various sizes, so as to formlayer above layer of a metal “cladding” above a component. The claddingof the invention can also be multi-level and include both a coarse basecladding (thickness in the order of millimeters) as well as a finecladding (thickness in the order of 100 microns) and/or a super-finecladding (thickness in the order of tenths of micron or even less).

According to a first aspect, the present invention refers to a methodfor providing a structural joint between two components of metalmaterial, in particular in the assembly of a motor-vehicle body or asubassembly thereof, wherein the method comprises the step of performingan electrical resistance welding spot between said components, and isfurther characterized in that it comprises the additional step ofapplying a “cladding” of metal material above said electrical resistancewelding spot, by means of additive manufacturing technology.

According to this first aspect, the invention is preferably furthercharacterized in that the aforesaid cladding application step by meansof additive manufacturing technology comprises a first step for applyinga coarse base cladding and a second step for applying a fine cladding,including the distribution of stiffening micro-ribs, above the basecladding.

Still preferably, these micro-ribs are formed according to an irregularhoneycomb pattern, with relatively thin walls, which may have across-section with uniform or variable shape and dimensions along theheight of the wall.

The Applicant's studies and experiments have shown that application ofthe above-described method to motor-vehicle body components consistingof galvanized steel sheet metal can result in local destruction of theouter layer of zinc due to the heat generated during the additivemanufacturing method. To overcome this drawback, according to apreferred embodiment of the invention, the method is furthercharacterized in that the step of applying cladding by additivemanufacturing comprises an additional step for local application of azinc overlay, also using additive manufacturing technology.

Another possible disadvantage deriving from application of the heat usedduring the additive manufacturing method could consist of a decrease inthe strength characteristics of the metal sheet forming the component,due to the alteration of the microcrystalline structure obtained forexample through a previous quenching process. In order to overcome thispossible drawback, the method according to the invention is preferablycharacterized in that it also comprises a local quenching step obtainedby feeding a cold fluid over the cladding, immediately after thecladding application step.

Thanks to all the aforesaid characteristics, the method according to theinvention allows structural joints to be obtained between components ofmetal material having high strength characteristics, without detrimentto the lightness of the structure. The term “structural joint” refers,precisely, to a joint that not only fulfills the task of keeping the twocomponents of the joint rigidly connected to each other, but can alsoconstitute—in itself—a part of the assembled structure, which is alsoassigned a “structural” function, i.e. that can significantly contributeto the ability of the entire structure ti sustain all the stresses towhich it is subjected during use.

Due to this significant advantage, the above-described method is able toallow, in particular, the framing of a motor-vehicle body-in-white byapplying a lower number of electrical resistance welding spots comparedto those normally used in conventional methods.

The invention also enables the use of thinner sheets, thanks to thereinforcement obtained by depositing a multi-level cladding. Usingthinner sheets results in a reduction in weight, and a reduction inprocess costs, since forming the sheet metal is achievable with lowercycle times and lower process energy.

According to another aspect of the invention, the invention relates to aplant for producing motor-vehicle structures or sub-assemblies thereof,wherein said structures are assembled by providing one or more jointsbetween components using the above-defined method, characterized in thatit comprises a conveying device for advancing the structures to beassembled up to a framing station, which includes robots that carry outa plurality of electrical resistance welding spots, and one or morerobots that perform the aforesaid step of applying a base cladding byadditive manufacturing above the electrical resistance welding spots,said plant also comprising at least one completion station, downstreamof the framing station, which includes robots for the execution of saidadditional step of applying a fine cladding above the base claddingapplied in the framing station. Still in this step, local reinforcements(multilevel cladding) can be produced on planar or aspherical surfaces(curved surfaces with an undefined profile) and also on components farfrom the junction areas. In this way, it is possible to use and to formthinner sheets with lower energy costs and lower cycle times, with athickness reduced even by 50% compared to conventional solutions. Themultilevel cladding, in this case, must also be designed to counteractthe deformations resulting from thinning of the sheet itself.

According to another aspect, the invention also relates to a method forapplying a reinforcement of metal material to a component of metalmaterial, particularly in the construction of a motor-vehicle body or asub-assembly thereof. According to this aspect, the method of theinvention comprises the step of applying a reinforcement of metalmaterial above the metal component, by means of an additivemanufacturing technology, and is further characterized in that theaforesaid step of applying a reinforcement by additive manufacturingtechnology comprises a first step for applying a coarse base claddingand a second step for applying a fine cladding, including a distributionof stiffening micro-ribs, of the type that has already been describedabove.

Even in this case, the method according to the invention preferably alsoprovides an additional step for the local application of a zinc overlayand/or an additional local quenching step by applying a cold fluid abovethe aforesaid cladding immediately after the cladding application step.

According to another embodiment of this method, the aforesaidreinforcement is applied, by using an additive manufacturing technology,on said component before subjecting the component to a forming step in amold.

All the aforesaid characteristics of the method according to theinvention open the way to a series of major improvements in theproduction of motor-vehicle structures compared to the techniquescurrently used.

DETAILED DESCRIPTION OF THE INVENTION

Further characteristics and advantages of the invention will becomeapparent from the description that follows with reference to theattached drawings, provided purely by way of non-limiting example,wherein:

FIG. 1 is a schematic cross-sectional view of a welded joint of twometal sheet elements, after a first step of an embodiment of the methodaccording to the invention,

FIG. 2 is a schematic cross-sectional view of the same welded joint ofFIG. 1, after a second step of the method according to the invention,

FIG. 3 is a partial perspective view of a superstructure made in themethod according to the invention by additive manufacturing technology,

FIG. 4 illustrates a variant of FIG. 3,

FIG. 5 shows a cross-sectional view of a single cell forming part of thestructure of FIG. 4,

FIG. 6 is a perspective view of a seashell,

FIGS. 7 and 8 are perspective views of tools usable in the methodaccording to the invention,

FIG. 9 is a schematic plan view of the layout of a production line formotor-vehicles, which makes use of the method according to theinvention,

FIG. 10 is a schematic cross-sectional view of a reinforcement appliedabove a metal sheet component by means of the method according to theinvention,

FIGS. 11, 12 show two steps of the method of forming a metal sheetcomponent provided with a reinforcement obtained using the methodaccording to the invention, and

FIGS. 13-16 show another embodiment example of the method according tothe invention.

In FIG. 1, the reference number 1 indicates—in its entirety—a structuraljoint of two steel sheet components after a first step of the methodaccording to a first embodiment of the invention. Two steel sheetcomponents 2, 3 have respective flanges 2A, 3A rigidly connected to eachother by an electrical resistance welding spot W obtained by using aconventional electrical resistance welding head (not illustrated),including two electrodes that are pressed from opposite sides againstthe two flanges 2A, 3A so as to exert a pressure and simultaneouslycreate a flow of electric current through these flanges to produce localfusion of the metal in their contact zone.

According to a first aspect of the invention, above the welded joint ofthe two flanges 2A, 3A, a coarse base 4 cladding is applied by additivemanufacturing technology.

FIG. 7 of the attached drawings shows, by way of example, a device 5 foradditive manufacturing, comprising a head 6 arranged at the end of aflexible tube 7 of elastomeric material, inside which a duct 8 for theaddition of metal powders, an optical guide 9 for transmitting a laserbeam and a duct 10 for feeding zinc powder are arranged.

According to a technique known per se, the device 5 feeds metal powdersthrough the duct 8, which are immediately melted above the sheet metalcomponents 2, 3 by means of the laser beam transmitted by the opticalguide 9, so as to form, layer by layer, the coarse cladding base 4having the required configuration.

In another embodiment, the powder can be replaced by wire. In this case,one or more coils of metal wire (or of polymeric material in themulti-material version) are provided, of various diameters (from 1millimeter to 10 microns) and different chemical composition, for thepossible production of cladding at multiple finishing levels (from 1 ton levels).

According to this embodiment of the method of the invention, once thebase cladding 4 is applied, the device 5 is used to apply a furtheroverlay of fine cladding 11, including a distribution of stiffeningmicro-ribs above the base cladding 4.

FIG. 3 shows a first example of a fine cladding structure having aplurality of micro-ribs 12 defining a general irregular honeycombpattern, including a plurality of cells 13. In the example of FIG. 3,the pattern has a two-dimensional configuration, in the sense that themicro-ribs 12 have a cross-section with a uniform shape and dimensionsalong their height.

FIG. 4 illustrates a variant of FIG. 3, in which the walls 12 have across-section with variable shape and dimensions along the height,according to the example illustrated, on an enlarged scale, in FIG. 5.

The Applicant has drawn inspiration for the design of the fine overlay11 from the existence in nature of shell structures of the typeillustrated in FIG. 6, which are characterized by an ideal combinationof structural strength and lightness.

Thanks to the characteristics described above, the welded joint Wcompleted at least with the coarse base cladding 4, and preferably withthe fine cladding 11 as well, becomes a “structural” junction that isable to constitute a part that provides a significant contribution tothe structural strength of the entire assembly.

A possible disadvantage of the method described above, which has beenidentified by the Applicant, is that the heat applied during theadditive manufacturing step to the metal sheet structure can locallydestroy an outer layer of zinc of which the sheet metal components 2, 3can be provided with, and may furthermore jeopardize the advantages ofstructural strength of the sheets 2, 3 obtained by means of a quenchingmethod to which said components have been previously subjected.

To overcome these drawbacks, the device 5 can include the duct 10 thathas been mentioned above, for the addition of zinc powders, which arealso applied with the additive manufacturing technique above thecomponents, in order to restore the zinc coating above the joint coatedwith the layers 4 and/or 11. Furthermore, it is also possible to providea device 5 of the type illustrated in FIG. 8 mounted, for example, onthe wrist of a manipulator robot 14 (only partially visible in FIG. 8)and, in addition to the head 6 that has been described with reference toFIG. 7, it is also provided with a nozzle 15 for the addition of a coldfluid (for example nitrogen or argon) over the components 2, 3 in orderto cause abrupt cooling of the components after the heating generated inthe additive manufacturing step, so as to obtain local quenching of themetal components.

The method according to the invention allows the manufacturing ofmotor-vehicle structures, in particular the framing of motor-vehicle“bodies-in-white” with a lower number of electrical resistance weldingspots, compared to conventional methods.

For example, with reference to FIG. 9, a motor-vehicle production plantcan provide a line 16 on which the structures to be assembled proceed,for example conveyed on vehicles of the automated-guided type 18. Alongthe line 16, the vehicles 18 encounter a framing station F comprisinglocking devices of any known type (not illustrated) for locking theparts constituting the structures to be welded in a precise assemblyposition, and one or more welding robots 19 equipped with electricalresistance welding heads to perform a plurality of electrical weldingspots on the structure carried by the vehicle 18. The framing station Fmay also comprise a plurality of robots 20 carrying devices 5 of thetype described above with reference to FIG. 7, in order to apply, overthe welded joints, a coarse layer of cladding, by means of additivemanufacturing technology, according to the expedients that have beendescribed above.

After leaving the framing station F, the welded structure transfers to acompletion station S, in which additional robots 21 execute theapplication of the additional layer of fine cladding, again by means ofadditive manufacturing technology. These robots can also perform therestoration step of an outer zinc layer above the welded joint and carryout local quenching, according to the method described above, in orderto restore the resistance characteristics of the sheet metal structures.

FIG. 10 shows a cross-section of a steel sheet component 22 on which alayer of coarse base cladding 23 and an overlap of fine cladding 24 havebeen applied, both with additive manufacturing technology, similar tothat been described above with reference to the welded joint of FIGS. 1,2.

If the metal sheet component 22 is a shaped component, it can beenvisaged that the layers of cladding 23, 24 are applied after formingthe sheet metal element, but a particularly interesting embodiment ofthe invention is where formation of the sheet metal component in a moldis carried out after applying the reinforcing element constituted by thebase layer 23 and by the overlap 24, which preferably has aconfiguration of the type that has been described above with referenceto FIG. 3 or to FIG. 4.

A variant of this embodiment is illustrated in FIGS. 11 and 12. TheseFigures show formation of a sheet metal component 22 in a mold having anupper mold 25 and a lower mold 26. In the case illustrated in FIGS. 11and 12, before formation in the mold, a reinforcing element 23 isapplied above the sheet metal 22 by means of additive manufacturingtechnology. Subsequently to the application of the reinforcement 23, thestructure thus obtained is formed in the mold, by closing the twohalf-molds 25, 26 in such a way that the reinforcement 23 isincorporated into the thickness of the sheet 22.

FIGS. 13-16 show the subsequent steps of a further embodiment of themethod according to the invention which produces multi-level andmulti-material cladding.

FIG. 13 shows a first step of applying a first coarse metal claddingover the component 22, defining reinforcing metal portions 23 spacedapart from each other. FIG. 14 shows a second step of applicationbetween the reinforcing metal portions 23 of a support layer 27, of alighter material, chosen for example from plastics, light metal alloysand ceramic materials. FIG. 15 shows a subsequent step of applyinganother level of fine cladding 28, and FIG. 16 shows the application ofa superfine final cladding, to create layers 29 above the support layer28.

As is evident from the above, the method according to the inventionprovides—in its preferred embodiment—a multi-level cladding, in whicheach level is created with successive layers, by means of additivemanufacturing. The levels may all be of metal material or may be made ofdifferent materials and also comprise levels of synthetic material orceramic material. Preferably, in addition, the various levels have aprogressively smaller dimension in height, starting from the base level,which can be a coarse cladding, with a height in the order ofmillimeters (that is, between 0.1 mm and 10 mm), towards theprogressively finer upper levels, which may have a thickness in themicron range (between 1 micron and 200 microns) and then in the order of10ths of microns (between 0.1 micron and 1 micron) or even less.

As is clear from the above description, the method according to theinvention opens the way to a series of improvements in the productionprocess of motor-vehicles, above all, in terms of an ideal combinationof strength and lightness of the obtained structure. Moreover, as isevident from what has been described, the method according to theinvention is easily applicable and adaptable to the production plantscurrently in use, without high costs.

Of course, without prejudice to the principle of the invention, theembodiments and the details of construction may vary widely with respectto those described and illustrated purely by way of example, withoutdeparting from the scope of the present invention.

1. A method for making a structural joint between two components ofmetal material, said method comprising: carrying out an electricalresistance welding spot between said two components, and applying acladding of metal material above said electrical resistance weldingspot, by utilizing additive manufacturing technology.
 2. The methodaccording to claim 1, wherein said applying the cladding of metamaterial by utilizing additive manufacturing technology comprises afirst step of applying a coarse base cladding and a second step ofapplying a fine cladding, including a distribution of stiffeningmicro-ribs, above the base cladding.
 3. The method according to claim 2,wherein said micro-ribs define an irregular honeycomb pattern with aplurality of cells whose walls have a cross-section of uniform orvariable shape and size along a height of said micro-ribs.
 4. The methodaccording to claim 2, further comprising a final step of localapplication of a zinc overlay.
 5. The method according to claim 1,further comprising a local quenching step, obtained by feeding a coldfluid above the cladding, immediately after application of the cladding.6. The method according to claim 1, wherein said joint is createdbetween two metal sheet components, before subjecting a structure formedby said two sheet metal components to a forming step in a mold.
 7. Aplant for producing motor-vehicle structures or sub-assemblies thereof,wherein said structures are assembled by providing one or more jointsbetween components by the method according to claim 1, wherein the plantcomprises: a conveying device for advancing structures to be assembledup to a framing station which includes robots, which carry out aplurality of electrical resistance welding spots, and one or more robotsperforming the first step of applying the base cladding above theelectrical resistance welding spot utilizing additive manufacturingtechnology, and at least one completion station, downstream of theframing station, which includes robots for executing said second step ofapplying the fine cladding above the base cladding applied at theframing station.
 8. A structure comprising at least two components,joined together by the method according to claim
 1. 9. A method forapplying a reinforcement of metal material to a component of metalmaterial, said method comprising: applying a reinforcement cladding ofmetal material above said component using additive manufacturingtechnology, which includes a first step of applying a coarse basecladding and a second step of applying a fine cladding including adistribution of stiffening micro-ribs.
 10. The method according to claim9, wherein applying the reinforcement cladding of metal material abovesaid component using additive manufacturing technology comprises athird, final step of local application of a zinc overlay.
 11. The methodaccording to claim 9, further comprising a local quenching step obtainedby feeding a cold fluid above said cladding immediately after applyingsaid cladding.
 12. The method according to claim 9, wherein saidreinforcement cladding is applied on said component before subjectingthe component to a forming step in a mold.
 13. The A method according toclaim 9, wherein the first step of applying the course base claddingincludes applying a first coarse metal cladding above said component,defining reinforcing metal portions spaced apart from each other, themethod further comprising applying a support layer between saidreinforcing metal portions, the support layer being of a lightermaterial than the course base cladding, and wherein the second step ofapplying the fine cladding includes one or more subsequent steps ofapplying one or more additional levels of fine and/or superfinecladding, above said reinforcing portions and said support layer. 14.The method according to claim 9, wherein said coarse base cladding has aheight on the order of millimeters, said fine cladding has a height onthe order of microns and wherein above said fine cladding, at least oneadditional super-fine cladding is applied with a thickness on the orderof tenths of a micron, each cladding being formed by one or more layersapplied by an additive manufacturing technology.
 15. A motor-vehiclecomponent, obtained by the method according to claim 9.